The Arctic wind blows hard on the snow-covered plains a few hundred miles southwest of Prudhoe Bay. It’s eight degrees in the winter chill. Despite global warming, I am still quite cold. I watch the tracks of the grizzly bear disappear upslope as they narrow toward a newborn calf. Out of my field of vision its mother, a muskoxen – the quintessential land animal of the Arctic – stands guard. But it is no match for the powerful predator looking for its next kill.
About 3,500 years ago, the last woolly mammoths died on a distant Arctic island in the Chukchi Sea. Muskoxen—mammoths’ shaggy-coated Pleistocene contemporaries—still roam the Alaskan Arctic today. Muskoxen are known to many for their distinctive huddling behavior evolved for defense against predators like grizzly bears and wolves. Recently this prey-predator relationship has itself become the focus of a discussion on conservation tools and approaches. Continue reading →
Mark D. Bertness, an ecologist at Brown University, began studying the salt marshes of New England in 1981. Twenty-six years later, in 2007, he started to watch them die. In one marsh after another, lush stretches of cordgrass disappeared, replaced by bare ground. The die-offs were wiping out salt marshes in just a few years.
“It’s unbelievable how quickly it’s moved in,” Dr. Bertness said.
Scientists have been witnessing a similar transformation in a number of plant species along coastlines in the United States and in other countries. And in many cases, it’s been hard to pinpoint the cause of the die-off, with fungal outbreaks, pollution, choking sediments stirred up by boats, and rising sea levels proposed as killers.
There is much at stake in the hunt for the culprit, because salt marshes are hugely important. They shield coasts from flooding, pull pollutants from water and are nurseries for many fish species.
In the journal Ecology Letters, Dr. Bertness and his colleagues have nowpublished an experiment that may help solve the mystery. The evidence, they say, points to recreational fishing and crabbing. A fisherman idly dangling a line off a dock may not appear to be an agent of ecological collapse. But fishing removes the top predators from salt marshes, and the effects may be devastating.
Once New England salt marshes started dying off, Dr. Bertness and his colleagues embarked on a broad survey. Quickly they noticed a difference between healthy marshes and sick ones. The dying marshes tended to be near docks, marinas or buoys where boats could anchor, or where there were other signs of fishing.
“It wasn’t a brilliant thing we thought of sitting around the lab,” Dr. Bertness said. “By the time we got to 10 marshes, we realized there was this huge disparity.”
Dr. Bertness and his colleagues wondered how fishing and crabbing were affecting the food webs of the salt marshes. If people pull out striped bass and blue crabs and other predators from a salt marsh, the animals’ prey species — including those that feed on plants, like marsh crabs — are left to thrive. A growing population of marsh crabs might wipe out the cordgrass in a marsh. Without the roots of the cordgrass to anchor the soil, the marsh would erode, making it harder for new plants to grow.
To test this idea, Dr. Bertness and his colleagues surveyed salt marshes in Narragansett Bay in Rhode Island, comparing marshes that were healthy with ones that were almost entirely dead. The scientists found that in dying marshes, the plants had more signs of being fed on by crabs. And when they looked for other proposed causes of marsh die-off, such as pollution, they didn’t find a correlation. They published their results in March in the journal PLOS One.
Next, the scientists took a step beyond simply observing the die-offs: They tried to cause them. If the predator hypothesis was right, then creating a predator-free salt marsh habitat should lead to the disappearance of cordgrass.
In May 2013, the scientists installed cages in a healthy salt marsh on Cape Cod. Each cage was three feet on a side, with mesh walls and an open bottom. Marsh crabs could feed on the cordgrass inside the cages by burrowing up through the mud, and the wire mesh walls protected them from predators like fish and blue crabs.
The experiment quickly yielded results. In a matter of weeks, the cages were crowded with marsh crabs, and much of the cordgrass inside the cages was dying off. “We were planning on it being a two- or three-year experiment,” Dr. Bertness said. “But by the beginning of July, I thought, ‘My God, this is really going fast.’”
William J. Ripple, an ecologist at Oregon State University who was not involved in the research, said, “This is an important new scientific discovery for salt-marsh systems, and more generally for ecology.” Scientists like Dr. Ripple have argued that predators are important to the ecological health of other ecosystems. But it’s been difficult to test the hypothesis directly the way Dr. Bertness has.
Merryl Alber of the University of Georgia agreed that the experiment showed that removing predators could decrease salt marsh grass. But she was reluctant to draw big lessons from the study. “It is still a leap to connect dieback to recreational overfishing,” she said.
Wade Elmer, a plant pathologist at the Connecticut Agricultural Experiment Station in New Haven, thinks that the full story of the salt marshes’ decline is more complex than just fishing. Dr. Elmer has identified a new species of fungus that attacks cordgrass in New England salt marshes. He has suggested that the fungus may weaken the plants in a way that prevents them from making chemical defenses to ward off the marsh crabs.
“I think we all have our pet theories that explain what we see in our backyard,” said Dr. Elmer, “but these theories often fail as soon as we look elsewhere.”
Dr. Bertness doesn’t rule out the possibility that other factors are at play in the die-off of marshes. But he argues that fishing is having an enormous impact.
“The implications of these findings for the conservation of salt marshes are huge,” he said. “We need to maintain healthy predator populations.”
Young Leopard. Bwabwata National Park, Zambezi Strip (Namibia). Credits: Ruben Portas
The world’s predators – mammals such as gray wolves, jaguars, tigers, African lions, European lynx, wolverines, and black and brown bears, along with sharks – are declining at an alarming rate. While those species are suffering for a variety of reasons, one of the main sources of mortality is human in origin. It’s a bit counterintuitive, since predators are some of the more charismatic of species. And charismatic critters are the easiest ones about which to convince people to care.
It would seem as if the best way to ensure the success of conservation programs aimed at preserving these most iconic of species would be to turn humans from enemies into allies. In other words, humans have to become more tolerant of predators. The problem, according to researchers Adrian Treves and Jeremy Bruskotter, is that we don’t know very much about what makes people tolerant of some predators and intolerant of others. In an article in this week’s issue of Science Magazine, they argue that wildlife conservation efforts ought to account for human psychology.
One of the primary assumptions driving research in conservation psychology is that intolerance toward predators, whether in the form of sanctioned eradication programs or culls (like gray wolves in the US orbears in parts of Europe or sharks in Australia) or in the form of illegal poaching, is driven mainly by the real or imagined need to retaliate against losses of livelihood, usually due to livestock predation. “Under this assumption,” Treves and Bruskotter write, “governments and private organizations aiming to protect predators have implemented economic incentives to reduce the perceived costs of predator conservation and raise tolerance for predators.”
One such program is implemented in Sweden. The government pays indigenous reindeer herders called Sami to tolerate the occasional loss of livestock to predators, and it seems to be effective for wolverines, brown bears, and lynxes. Each time a predator successfully reproduces, the Sami herders are paid.
But that strategy is only effective insofar as the source of predator intolerance is economic. That might work for some predators, but not for others. Fifty-one percent of Sweden’s wolves died from poaching between 1998 and 2009. The Swedish program has so far failed to protect gray wolves because the Sami perceive the costs of tolerance as weightier than the benefits. At present, wolves are effectively extirpated from parts of the country where reindeer graze.
An adjustment of social norms may succeed, however, where economic incentives fail. In Kenya, Maasai herders are not just compensated when lions kill their livestock; some community members are trained to warn villagers when lions approach, and monitor their movements. It reflects a different strategy, one of cautious coexistence driven by altered social norms rather than rigid defensiveness driven by externally imposed economic remuneration.
A similar effort is implemented in Brazil, for ranchers whose livestock graze near jaguar territories. In one study, researchers interviewed 268 cattle ranchers about their tolerance for jaguars, and found that perceived social norms were far more influential than economic disincentives when it came to determining any individual rancher’s likelihood to kill a jaguar. In other words, if ranchers thought that their neighboring ranchers killed jaguars, or if they thought that their neighbors would expect them to kill jaguars, they were more likely to do it. It’s the very same peer pressure that plays out in high schools across America, superimposed onto Brazilian rainforests. “The social facilitation that results in areas where poaching is common and accepted can create predator-free zones as neighbors and associates coordinate their actions explicitly or tacitly,” write Treves and Bruskotter.
Things aren’t so different in the industrialized West, where sport hunters are often thought of as valuable partners in conservation. The reasoning goes that since hunters at one time helped to conserve game species (like deer and ducks), then hunters would also help conserve predators who are designated as legal game. One program in Wisconsin was designed explicitly to increase tolerance for wolves by allowing 43 of the endangered canids to be killed each year. And yet while the program was in place, researchers found a decrease in tolerance and in increase in the desire to kill wolves. Legalizing the hunting of predators, even in a restricted way, didn’t have the intended outcome.
Wisconsin’s wolf hunting program wasn’t a controlled experiment, so the interpretation of the results is necessarily limited. However, some researchers did organize a controlled experiment to see how various approaches might improve tolerance for American black bears. The researchers discovered that providing people with information about the benefits derived from bears along with information about how to reduce the risks of negative bear encounters increased peoples’ tolerance for the animals. On the other hand, information about how to reduce risks alone, without the additional information about benefits, actually reduced their tolerance. Treves and Bruskotter suspect that’s because the risks were made more salient without the buffering effect of the bears’ benefits on local ecosystems. Similar results were seen for studies investigating the tolerance of tigers in Nepal.
Taken together, Treves and Bruskotter argue that while monetary incentives can be successful tools in the conservationist’s toolbox, poaching is influenced more strongly by social and cultural factors. “We therefore recommend caution in legalizing the killing of predators,” they say. They further argue that the best way to move forward in understanding when economic and social incentives are more or less effective is through explicit experimental manipulation, rather than through the haphazard patchwork of trial and error that has in many cases characterized predator conservation efforts. – Jason G. Goldman | 2 May 2014
Source: Treves A. & Bruskotter J. (2014). Tolerance for Predatory Wildlife, Science, 344 476-477. DOI:10.1126/science.1252690
Sometime last weekend a three-meter female tiger shark snared itself on a hooked line that was attached to a floating drum just off the southwestern coast of Western Australia. A commercial fisherman later motored by and, with the blessing of the government, shot it in the head. Four times.
The controversial cull began this weekend as a response to the deaths of seven people over the past three years at the hands – er, teeth – of sharks in Western Australia. At a press conference the state’s premier, Colin Barnett, said, “I get no pleasure from seeing sharks killed, but I have an overriding responsibility to protect the people of Western Australia, and that’s what I’m doing.” Protecting swimmers and other beachgoers is indeed important, but are culls even effective in the first place? And are there other methods that are better able to both protect swimmers and the sharks that many would rather avoid?
While the scientific data on the effectiveness of shark culls is scant, what data is available suggests that they aren’t terribly effective. In a 1994 paper in the journal Pacific Science, University of Hawaii researchers Bradley M. Wetherbee, Christopher G. Lowe, and Gerald L. Crow took stock of nearly two decades of shark control programs in Hawaii.
The programs were implemented with two main objectives. The obvious aim was to reduce the number of sharks in the water. In addition, data was collected from the sharks that were captured in order to add to the body of knowledge on shark biology. If the sharks were going to be killed, at least scientists could benefit from the data. At least, that was the idea.
But Wetherbee and colleagues reported that only one scientific paper derived from the shark cull data was ever published. As a result, the reports made by those who carried out the culls went unchallenged by the formal peer review process. And while the reports declared the culls successful insofar as fewer sharks were caught as time went on, a correlation does not prove causation. The researchers point out that while “the removal of nearly 4700 sharks from Hawaiian waters over an 18-yr period undoubtedly resulted in a substantial decrease in the population, and declines in shark abundance are evident in reduced catch rates in long-running programs,” other factors that could have contributed to that decline were never considered, such as predictable seasonal shifts in local shark populations, or weather patterns, which not only drive changes in shark behavior but also have a tendency to foul fishing efforts.
More damning evidence comes from the finding that there was no statistical difference between the average number of attacks per year for the eighteen years prior to the first control program and the eighteen years in which control programs were intermittently implemented. “Consequently,” Wetherbee writes with an excessive amount of understatement, “conclusions made about the effectiveness of the programs in reducing shark populations might well have been stated with less confidence.”
If culls don’t seem to work, are there any other methods for making swimmers safer? Gill nets have been shown to be effective at reducing shark encounters, but they have the downside of indiscriminately catching dolphins, dugongs, turtles, birds, rays, tuna, other non-dangerous sharks, and even whales as well. And the removal of larger sharks from the sea by drowning them in gill nets has led to the proliferation of smaller sharks in some areas, which in turn compete with fishermen for the same fish stocks. Indeed, removing apex predators can have widespread effects on the entire ecosystem, something that was made obvious with the removal and subsequent reintroduction of wolves fromYellowstone National Park.
A 2013 paper in the journal Animal Conservation describes a more welfare-oriented, ecologically conscious approach to shark attack mitigation in Recife, Brazil. The problem was that 55 shark attacks were recorded along a twenty-kilometer stretch of coastline between 1992 and 2011, 19 of which resulted in fatalities. As a result, the state government created a Committee for the Monitoring of Shark Attack Incidents, which formulated a new strategy to manage the risk of shark attacks. The guiding principle was removing sharks from high-risk areas rather than from their populations. It was actually quite simple: sharks were captured, transported, and released farther from shore. If effective, the reasoning went, such a strategy would reduce the risk of shark-human encounters while also maintaining the structure of coastal ecosystems.
Not only did the catch-and-release method avoid creating a massive ecological upset, but it was also overwhelmingly effective. Between 2004 and 2011, the shark relocation program was in operation for 73 months, and was inactive for 23 months due to funding shortfalls. Thus, researchers were able to compare the frequency of shark attacks while the program was active to months it was on hold. While the program was operational, Recife saw an impressive 97% reduction in the monthly shark attack rate.
While the shark cull program began in Western Australia last week, groups of Japanese fisherman continued their annual dolphin slaughter. It is perhaps not surprising that the kind of outrage directed towards the Japanese town of Taiji has not been aimed towards Western Australia. The cultural narrative that surrounds dolphins is one of friendliness. Dolphins are thought of as smart, playful tool-users, their faces plastered in a permanent smile. Sharks, on the other hand, are traditionally seen as little more than sets of flesh-shredding steak knives with fins. Of course neither tale is complete. Dolphins can bejerks and sharks can actually be quite clever. As shark scientist David Shiffman wrote in a recent blog post, perhaps the best strategy to avoid the needless slaughter of sharks is simply better education. Maybe swimmers can simply be taught the most effective behaviors for reducing the risk of an unfortunate encounter. Combined with a catch-and-release program, humans could then safely enjoy our brief visits to the sea. – Jason G. Goldman | 29 January 2014
Sources: Wetherbee B.M., Lowe C.G. & Crow G.L. (1994). A Review of Shark Control in Hawaii with Recommendations for Future Research, Pacific Science, 48 (2) 95-115.
Hazin F.H.V. & Afonso A.S. (2013). A strategy for shark attack mitigation off Recife, Brazil, Animal Conservation, n/a-n/a. DOI: 10.1111/acv.12096
F109, a six-year-old cougar, nursing three three-week-old kittens. She wears a Vectronics satellite collar which allows researchers to follow her movements in near real time and study the secret lives of mountain lions. Photograph by Mark Elbroch/Panthera
Wolves are coursing, social predators that operate in packs to select disadvantaged prey in open areas where they can test their prey’s condition. Mountain lions are solitary, ambush predators that select prey opportunistically (i.e., of any health) in areas where slopes, trees, boulders, or other cover gives them an advantage. Thus, wolves and cougars inhabit and utilize different ecological niches, allowing them to spatially and temporally coexist; nevertheless, in the absence of wolves, cougars utilize areas traditionally assumed to be the sole dominion of coursing wolves. This suggests that where wolves are sympatric with cougars, wolves limit mountain lions.
In fact, wolves kill mountain lions. This has never been disputed. Wolves are considered the dominant competitors in most interactions between the species. Take for instance, the Hornocker Institute study of mountain lions in Northern Yellowstone led by Dr. Toni Ruth, in which researchers discovered the remains of three mountain lions killed by wolves. What is contentious is the idea that mountain lions might kill wolves.
Look carefully for the mountain lion in the background, pushed off its kill by a large wolf caught on remote camera. Photograph courtesy Teton Cougar Project/Panthera
Liz Bradley, a Montana Fish, Wildlife and Parks wolf biologist, reports that she has discovered five wolves killed by mountain lions in three years—all bearing the characteristic canine punctures in their skulls betraying the identity of the perpetrator. Some dispute her claims and point out that wolves fight each other too, especially adjacent packs, and that they also attack the head; skeptics believe a canine puncture in a wolf skull could be made by another wolf just as easily as a mountain lion.
The Teton Cougar Project operates in the Southern Yellowstone Ecosystem, and is one of very few long-term studies of mountain lions. Since the start of the project, wolves have trickled into the area, established territories and reproduced. In 2001, U.S. Fish and Wildlife Service surveys estimated that there were about 10 wolves in our study area, and that number steadily increased to as high as 91 in 2010. To date, we’ve documented five lions killed by wolves, all kittens, and all less than six months old while they were still relatively slow to climb and less than fully coordinated. But it was just last October that we finally documented the contrary. For the first time, a mountain lion we were tracking killed a wolf.
She’s a particularly feral mountain lion, F109, an adult female with three three-month-old kittens. All cougars are feral, of course, but there’s something unique about F109. She has “crazy” eyes, and always wanders the most rugged, inhospitable terrain. She was near impossible to catch in the first place. She’s a survivor.
We can’t tell you exactly what happened, but we can describe what we deciphered from the clues left behind in the snow. F109 was up high traversing steep, barren slopes, where we expected there was little game. Nevertheless, her location data indicated that she’d stopped and we suspected she’d made a kill. We slogged up the mountain to investigate, the ground bare of snow adjacent the road, but as deep as our thigh in the high bowl where she lingered. The entire area preceding her position was a mosaic of wolf tracks and trails. A wolf pack made up of adults, subadults and pups had criss-crossed the area, leaving barely a patch of snow without their sign.
Perhaps the wolves had challenged F109, or perhaps just one of them wandered too close to her kittens, or perhaps a pup felt like exploring on its own—trying to decipher the absolute pandemonium of tracks was beyond us. Whatever the circumstances, F109 captured and killed a pup born this year just above the chaos of wolf activity. By this time (November), wolf pups are sizable, their skulls larger than those of coyotes. We discovered the signs of struggle, the telltale blood in the snow, and the pup’s remains beneath a lonely subalpine fir: a pile of coal black fur, bone shards from the legs, and the skull, skinned but completely intact. F109 and her kittens had consumed the pup completely.
Thus far, our research has supported exactly what everyone expected: Wolves dominate mountain lions in most encounters. But, this recent exchange is particularly exciting. No longer can we say that wolves dominate mountain lions in all encounters. What circumstances led to F109 turning the tables, we do not know. Perhaps F109’s predecessors served as naïve intermediaries relearning to coexist with a dominant competitor, a species absent since 1926, when the last wolf was killed in Yellowstone National Park. Perhaps F109 is evidence that lions learn quickly and adapt, and that mountain lions will successfully coexist with wolves in the Yellowstone Ecosystem for generations to come.
For at least 30 years, scientists have believed that cheetahs fail to catch their prey more often than other big cats because they overheat at high speeds. But researchers in Namibia who implanted sensors in six cheetahs tell a different story. Even when one of the study animals came close to the maximum chase distance ever reported for a cheetah, his body temperature did not exceed that of his regular 24-hour average. After the hunt, cheetahs’ temperatures rose slightly, more when the hunt was successful than when it was not. The researchers attribute this temperature increase to the stress of protecting a kill from other predators.
Hunting cheetah reportedly store metabolic heat during the chase and abandon chases because they overheat. Using biologging to remotely measure the body temperature (every minute) and locomotor activity (every 5 min) of four free-living cheetah, hunting spontaneously, we found that cheetah abandoned hunts, but not because they overheated. Body temperature averaged 38.4°C when the chase was terminated. Storage of metabolic heat did not compromise hunts. The increase in body temperature following a successful hunt was double that of an unsuccessful hunt (1.3°C ± 0.2°C versus 0.5°C ± 0.1°C), even though the level of activity during the hunts was similar. We propose that the increase in body temperature following a successful hunt is a stress hyperthermia, rather than an exercise-induced hyperthermia.